Matagorda Bay (at 28°38' N, 96°15' W) is a major bay on the Texas coast protected from the tides and storms of the Gulf of Mexico by the Matagorda Peninsula. The bay is divided almost equally between Calhoun and Matagorda counties. Tres Palacios Bay, Turtle Bay, Carancahua Bay, Keller Bay, Cox Bay, and Lavaca Bay all open into Matagorda Bay. Matagorda Bay is also crossed by the Gulf Intracoastal Waterway and the ship channels to Palacios, Port O'Connor, and Port Lavaca. All of these channels have spoil banks alongside. The only entry to Matagorda Bay from the Gulf is through Cavallo Pass at the southern end of Matagorda Peninsula, or the Matagorda Ship Channel. At the north end of the bay an isthmus formed by Egret Island and the extended banks of the Colorado River connect the mainland to Matagorda Peninsula and separate Matagorda Bay from East Matagorda Bay.
Matagorda Bay has gone by the name Espíritu Santo and later by the name Costa y Bahía de San Bernardo, both of which seem to have designated the general area. The first reference to what may be Bay Espíritu Santo appears on a map by Alonzo Álvarez de Pineda in 1518–19; in 1681 the map by Ángel de Villafañe and Jorge Serón shows a bay in the same place. René Robert Cavalier, Sieur de La Salle, entered the bay in 1685, after missing the Mississippi River, and established his colony at Fort St. Louis. Alonso De Leon entered the bay after his discovery of La Salle's colony in 1689. The Union Navy entered Matagorda Bay in 1862 and bombarded Port Lavaca on October 31 and November 1. The bay continues to contribute to the Texas economy. Goods weighing more than four million tons were shipped through Port Lavaca in 1985.